Apparatus for screening granular materials



' May 22, 1923.

R. A. LEAHY APPARATUS FOR SCREENING GRANULAR MATERIALS Filed March 28 1921 2 Sheets-Sheet 1 Fig.4

Fig.5

lNvEnToR ATTORNEYS May 22,1923. 1,456,067

R. A. LEAHY APPARATUS FOR SCREENING GRANULAR MATERIALS Filed March 28 1921 2 Sheets-Sheet 2 Fig. 5

Fig.6

INVENTOR R.A.Leahy ATTORNEYS Patented May 22, 1923.

UNITED STATES RICHARD A. LEAHY, OF BONNIE TERRE, MISSOURI.

APPARATUS FOR SCREENING GRANULAR MATERIALS.

Application filed March 28, 1921.

To all whom it may concern Be it known that I. Riemann A. Learn, a subject of Great Britain. residing at Bonne Terre. Missouri, have invented a certain new and useful Improvement in Apparatus for Screening (iranular Materials. of which the following is a full, clear. and exact description, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to the art of screening granular materials.

()no object of my invention is to provide an appa'atus fo screening granular materials that causes the )articles of the ma-- terial to be Stratified according to their relative masses (or sizes, ii the material is homogeneous) in such a way that the. heaviest or coarsest particles of the material will be forced upwardly to the top of the layer of material and the lightest or finest particlcs will be brought in direct contact with the screening medium, thereby causing the lightest or finest particles of the material to pass through the meshes or openings in the screening medium without hindrance by the particles which are too large to pass through said openings or meshes.

Another object is to provide an apparatus for screening granular materials that materially increases the eliiciency of the screen ing medium and overcomes the necessity of discontinuing the screening operation at frequent intervals and cleaning the screening medium. as is necessary with the methods heretofore in general use.

Other objects and desirable features of my invention will be hereinafter pointed out.

Briefly described, my improved apparatus consists of a flexible screening medium that is held under tension, and means for "subjecting said screening medium to such Serial No. 456,431.

a layer and flow downwardly over same by gravity, and said screening medium is subjected to-a differential vibrating motion at one or more points. so to cause a slow downward movement and a quick or sudden upward movement of the screening medium, thereby causing the heaviest particles of the material to be moved upwardly into a position where they will not obstruct the passage of the finer particles of the material through the screening medium. This treat ment of the material being screened not only causes the particles to be stratified ac ord ing to their relative masses or sizes and insures the lightest or finest particles passing freely through the screening material without hindrance by the particles which are too large to pass through the meshes of the screening medium. but it also prevents the openings or meshes of the screening medium from becoming permanently blinded or clogged by particles of material of approximately the same size as the meshes but which are just too large to pass through the meshes. Accordingly, my apparatus increases the efliciency of the screening medium and decreases the screening area necessary. by bringing the smallest particles in direct contact with the openings or meshes in the screening medium. and it overcomes the necessity of discontinuing the screening operation at frequent intervals and cleaning the screening medium so as to remove the particles that have become clogged in the openings or meshes of the screening medium.

Various forms of apparatus may be used to practice my method. but I prefer to use an apparatus that comprises a flexible screening medium stretched taut between two points and arranged in an inclined position. and means for imparting a differential vibrating motion to one or more zones of said screening medium extending transversely across the entire width of same so as to obtain a comparatively slow movement downwards and an accelerated, quick movement upwards beneath the layer of material resting on the screening medium.

Figures 1 and 2 of the drawings are diagrammatic views. illustrating the principle on which my apparatus operates.

Figure 3 is a front end elevational view of the apparatus.

Figure 4 is a longitudinal sectional view of said apparatus.

Figure is an enlarged top plan view of a portion of said apparatus.

Figure 6 is a transverse sectional view, taken on the line 6-6 of Figure 5; and

5 Figure 7 is a longitudinal sectional view,

taken on the line 7-7 of Figure 6.

In Figures 1 and 2 tr designates a flexible screening medium that is held in tension between the fixed lines of support A-A and 0 BB. A differential vibrating motion is applied to the screening medium m at one or .morc points extending transversely across the entire width of said screening medium so that it obtains a comparatively slow movement downwards, represented by the arrow m in. Figure 1, and an accelerated. quick movement upwards, indicated by the arrow n, beneath the la 01'' of material resting on the screening me ium The effect of this differential motion on'the particles of material on the screening medium is to throw them upwards with a force proportional to their masses (or sizes, if the material is homogeneous), the heaviest or coarsest particles of the materialbeing forced to the top of the layer and the lightest o1 finest particles coming in contact with the semen ing medium and passing freely through the meshes or openings in same without bein hindered by those particles of materia which are too large to pass through said meshes. This difl'erential vibrating motion also prevents the openings of the screening material from becoming permanently blinded by particles that are just too largeto pass through said meshes. as any particles likely to catch in the meshes are thrown upwardly by the accelerated motion', represented by the arrow 72 in Figural.

The screening medium a: is preferably in- ,clined downwardly from A to B, as shown in Figure 2, so as to cause the differential vibrating motion to also impart a forwardmotion to the particles of material remaining on top of the screening medium, thus causing the particles which are too large to pass through the meshes to be carried down- -vvardly by gravity and discharged at the lower end B ofthe screening medium.

When the material being screened is applied to the screening medium in a continuous stream, as is the usual practice in ore I and coal dressing plants, the finest particles of material immediately, pass through the openings or meshes in the screening medium on coming in contact with the upper end ortion ofthe screening medium 2:, thus,

caving the larger art of the screening area for the separation of those particles. more.

nearly the same size as the. opening or meshes through which they should pass. The stratification is completed on the lower end ortion of the screening medium whi 'h is su jected to the differential vibrating motion, said vibrating motion also preventmg the openingsof the screening medium from becoming permanently blinded or clogged with particles of the material.

In practice I prefer to apply the differential vibrating motion to only the lower end portion of the screening medium m, but in view of the fact that the screening medium is flexible and under tension, and is connected only at its opposite ends to the supporting structure which carries it, the entire screening medium will vibrate between the two points A and B, the minimum vibration being applied to the upper cnd portion of the scrcenin medium throu h which the finest particlcs .of the material pass, and the maximum vibration being-applied to the lower end portion of the screening medium over which the coarsest particles of the material travel. This zone of manimum vibration extends uniformly across the entire screening area, transversely of the direction of the material over the screening medium. Accordingly, all the particles passing through the zone of minimum vibration which are too large to escape through the meshes in the portion of the screening medium constituting this zone must pass through the zone of maximum vlbration bcfore reaching the point B of final discharge for the over-sized particles.

The apparatus can be constructed in various ways, but I prefer to equip it with a flexible screening medium :1; consisting of a strip of wire cloth or punched sheet metal suspended within a rectangularly-shaped frame composed of side pieces 1 and end pieces'2 arranged in an inclined position on a supporting structure 3, as shown in Figure 4. The lower end of the screening medium a: is preferably clamped between two transversely-disposedbars 4 that are permanently connected in any preferred manner to the frame within which the screening medium is arranged and the upper end of the perforated stripvzrthat constitutes the screening medium of the apparatus is clamped between two transversely.- disposed bars 5 that are connected by means of tension bolts 6 to the upper cross piece 2 of the reotangularly-shaped frame in which the screening medium is arranged. The tension bolts 6 not' only serve to hold the se'reening'medium under suflicient longitudinal tension to make said medium resilient, but they form uneasily adjustable means for varying the tension of thescreening medium. The screening medium a; is

preferably provided at its longitudinal side edges with u wardlyrojecting. flexible flanges 7, as siown in igure 6, so as to prevent the unscreened material from escaping from QthBSidG edges of the screening.

medium, but said side edges are not connected t the side'pieoes 1- ofthe frame in which t e screening medium is stretched.

I ll

Various means can be used for imparting the differential vibrating motion to the screening medium :r of the apparatus, but l'prefer to use a means consisting of a multiple toothed 'cam 8 connected to an operating shaft 9 and arranged to co-operate with a tappet 10 that is'connected by means of a rod 12 to a wooden cross beam 11 that extends transversely underneath the screening medium :1 across the entire width of same. The upper end of said rod is threaded into the tappet ll) and the lower end portion of said rod is secured to the cross beam by nuts or in any other suitable way. the cross beam being fastened to the screening medium a: by wooden screws or in any way that will cause the screening medium to vibrate when the cross beam 11 moves upwardly and downwardly. The tappct 10 is held against the face of the cam S by a leaf spring 13 rigidlv connected at one end to a transversely-disposed supporting member 14 arranged above the screening medium, said spring having its opposite end adjustably connected to the tappet rod 12 by means of nuts 15, which can be adjusted so as to vary the tension of the spring 13. At each cycle of operations of the shaft 9, the cross beam or member 11 will move downwardly slowly, followed by an accelerated upward movement that is suddenly arrested by the tappet 10 striking against the cam 8 which virtually acts as an anvil. thereby causing the particles of material on the screening medium to be thrown upwardly with a force proportional to the masses of said particles. The operating shaft 9 is journaled in bearings 16 on the transverselydisposed supporting member and is provided with a pulley 17 that is adapted to co-operate with a driving belt (not shown) the supporting member 14 being rigidly connected to the side pieces 1 of the frame in which the screening medium is stretched. \Vheu the apparatus is equipped with a twelvetoothed cam, the cam shaft 9 is preferably operated at about 200 R, P. M., so as to impart about 2400 vibrations per minute to the screening medium. If the cam 8 is equipped with teeth about of an inch high. the maximum vibration of the screening medium 0* will be about 3 of an inch vertically. The power consumption of such an apparatus is exceedingly slight.

as I have found that less than l H. le is sufficient to drive a 3 ft. screen at 2400 vibrations per minute with a full load.

In the various kinds of screening devices heretofore used for screening granular material the openings or meshes of the screening medium become blind after .a short period of operation. This blinding decreases the screening efliciency sometimes more than hen this occurs it is necessary to stop the screening operation and clear the openings or meshes of the screening medium by hammering the screening medium or striking it a blow with a stick or other device. Sometimes water sprays are used in wet screening in an endeavor to prevent the screening medium from becoming blinded or clogged, but it has been found that water sprays will not keep the screening medium clean and the meshes of same un obstructed. My improved apparatus overcomes the above-mentiouml characteristics of the screening device heretofore in use, as the differential vibrating motion which is applied to the screening medium prevents the particles of material from becoming clogged in the meshes of the screening medium. In fact, I have found in dry screening material of a damp or sticky nature. such, for example, as mine run ore containing three or four per cent moisture, the openings or meshes of the screening medium are kept free by the difl'erential motion which throws the lumps of damp material to the top of the layer on the screening medium, thus permitting the free particles to pass through the openings or meshes of the screening medium.

My invention not only increases the oiliciency of the screening medium of an apparatus used for screening granular material, and reduces the time required to screen such material, due to overcoming the necessity of discontinuing the screening operation at frequent intervals and cleaning the screening medium of the apparatus, but it also increases the speed of the material passing over the screening medium. thereby making it possible to diminish the slo e or angle of the screening medium of t; e apparatus and thus reduce the head room required in the mill for the apparatus.

Having thus described my invention, what I claim as new and desire to secure by Let ters Patent of the United States is:

1. An apparatus for screening granular material, comprising a flexible screening medium arranged in an inclined position and held under longitudinal tension, the side edges of said medium being free to vibrate, and means connected directly tosaid screening medium at a point intermediate its ends and extending transversely across the entire width of same for vibrating said medium upwardly-and downwardly so as to impart a comparatively slow ownward movement to said screening medium followed byan accelerated upward movement that is suddenly arrested, thereby causing the articles of material on said screening medium to be thrown upwardly with-a force proportional to the masses of said particles.

2. An apparatus for screening granular material, comprising a flexible screening medium arranged in an inclined position and held under longitudinal tension, the side edges of said screening medium being free to vibrate, a rigid member arranged transversely across said screening medium adjacent the lower end of same end connected 5 directly to said screening medium, and means for vibrating said member downwardly and upwardly comprising a part connected. to said member and a co-operating anvil against which said part strikes so as to suddenly k arrest the upward movement of said screening medium, thereby causing the particles of material on said screening medium to be ithrown upwardly with a force proportional to the masses of said particles. l5 3. An apparatus for screening granular material, comprising a stationary frame arranged in an inclined position, a piece of mesh material held in said frame under sufiicien't longitudinal tension to produce a flexible screening medium having inherent resiliency, the side edges of said screening medium being freeto vibrate, an operating shaft arrangql transversely of said frame, 'a transverselyidisposed, rigid member connected directly to said screening medium and extending across the entire width of' same, and means actuated by said operating shaft for imparting a differential vihrating motion to said transversely-disposed, rigid member comprising a part con nected to said member, and a co-operating anvil against which said part strikes so as to,

of said member to suddenly arrest the upmaterial, comprising a frame arran ed in an inclined position, a strip of ii exible screening, medium arranged between the side pieces of said frame in such a way that the side edges of said medium are free to Vibrate relatively to said side pieces, means for connecting the ends of said screening medium to the top and bottom cross pieces of the frame and holdin said medium under suflicient longitudina tension to make said medium resilient, a transversely-disposed, rigid member connectdddirectly to said screenin medium and extending across the entire wi th of same, an operating shaft supported at. a point above saidscreenin medium, and a tap d mechanism rated by said shaft for vi rating said mem r upwardly and downwardly, comprising a cam on the shaft and a co-operating part on said member that strikes against said cam with suflicient force during the upward movement 6O ward movement of the screening medium for the purpose described.

RICHARD A. LEAHY.

Certifichpe a: Corrcctlbn.

It is heraby certified that in Letters 'Pctent No. 1,455 067, granted Ma. 22 1923, upon the application of Richard A. 1mm, of Bonna rem, mm, or m imgfioi'en argdip' A paratus for Screening Granular Mnterialsflwriors 'ap air in e nn speci for a word end, secqnd occurrence, read and; same page inc 54, claim 4, 'for thc vmrd tapped read tappety and that the said Iatters-Iatent should be read with these' corrections therem that the same may conform to the record of the case in tha'Patent' Offiea. 1

Signed andseplcd this 17th day of July, A. D., 1923.

[ml-.1 WM. A. KINNAN,

. i Acting 'onwmfuiomr 0] Patents.

' cation requiring correction as follows: P 4, line 4, aim 2 

